Evaluate the following expression when $a = 1$ and $b = 2$. $3$ $a$ $ + 4$ $b$ $ + 7$
Solution: Substitute $1$ for ${a}$ and $2$ for ${b}$ $ = 3{(1)} + 4{(2)} + 7 $ $ = 3 + 8 + 7 $ $ = 18$